High quality, pure crystals are of great value for a variety of industrial and research applications. Crystallization is frequently used as a method of purification in the biotechnology and pharmaceutical industries. More highly ordered crystals will typically results in a more highly purified product. Larger crystals can also impart advantages in packaging and handling operations, and may have advantages for controlled release drug delivery media. The objective of the present proposal is to demonstrate that anti solvent crystallization using liquefied gases, compressed gases, or cortical fluids (which have properties intermediate to gases and liquids) is a generally useful technique for forming large, high purity crystals from therapeutic materials such as natural product anti-cancer agents and macromolecules such as insulin. In the anti solvent technique, the material of interest is first dissolved in a suitable organic solvent. The compressed/liquified gas, e.g., carbon dioxide, in which the compound of interest is poorly soluble, is then slowly added to bring about crystallization. The program may also be useful in obtaining large single crystals for X-ray structural analyses to determine molecular conformations. Proposed commercial applications: The proposed process can benefit the pharmaceutical and biotech industries by yielding improved purity of therapeutic products with less residual solvent contamination. The technique can be useful in obtaining a desired particle size in drug manufacture, and may also prove useful in terms of controlled release formulations such as microspheres.